Horton Brothers Flying Wings

[Henk]

, yes, it is strange that they do not care so much these days about stealth aircraf like they use to.

Henk

 

[Jarda Rankl]

And still some coloured picture.

 

[Henk]

Thanks mate for the great pics. I have seen small ones of this but these are nice and big.

Are you a fan of their work?

Thanks mate.

Henk

 

[Jarda Rankl]

Not really, Henk. I´m into WWII American planes. I just came across these colour photographs by chance and hoped someone could fin them useful. Despite the fact the activites of the Horten brothers are very interesting, the WWII period is such an extensive topic it makes me specialise. Therefore, I´m into Americans.

 

[Henk]

Wow, thanks mate they are truly great. Ya we all kinda like our own thing of WW2 hey.

I thought I knew a lot about WW2 but I learned I knew almost nothing. Never stop learning.

Thanks mate for the pics.

Henk

 

[Jarda Rankl]

And that exactly is the thing. I´ve been interested in WWII for more than 30 years and it was the understanding that I would not be able to reasonably cover the entire topic of WWII air war that made me decide to focus myself. My hobby is US planes and US Air Force operations in WWII, but I welcome information about planes and air forces of other countries as well. If you are interested in some specific items, I can send them to you, if I have them.

 

[Jarda Rankl]

And that exactly is the thing. I´ve been interested in WWII for more than 30 years and it was the understanding that I would not be able to reasonably cover the entire topic of WWII air war that made me decide to focus myself. My hobby is US planes and US Air Force operations in WWII, but I welcome information about planes and air forces of other countries as well. If you are interested in some specific items, I can send them to you, if I have them.

Jarda

 

[Henk]

I would like that very much mate I love any new info.

Henk

 

[Neilster]

I've some more images on another computer. I'll post them as soon as possible. I used fractal decompression software to enlarge some smaller Ho IX images and they look quite good.

Cheers, Neilster

 

[DerAdlerIstGelandet]

I agree that the whole topic is so vast to cover and therefor I specialize as well and I prefer to specialize in the Luftwaffe aircraft because it was just so crazy the things they would come up with. I do however love all of it and try to learn as much as possible about every nations aircraft in WW2.

The Horton Brothers were amazing in my opinion and it would have been interesting to see how the Ho-229 would have panned out.

 

[Henk]

That is one you see quite a lot on the net.

I got some more.

I wish I could work on the Horten 229 V3 restoration project when they start, to be able touch and see it for myself would be great.

 

[Neilster]

Righto. This is part one of something I found...

FARNBOROUGH HANTS
The Horten Tailless Aircraft
by K.G. Wilkinson, B.Sc. D.I.C.
Horten VIII IX
________________________________________
3.10 Horten VIII
General
This was to have been a flying model of a proposed six-engined trans-Atlantic passenger transport weighing 100,000 kg. The span was to be 40 m with an aspect ratio of 10 and sweepback of 28°. Power units were six Argus AS 10 C engines.
To make the aircraft attractive to R.L.M. and thus get backing for the project, the Hortens added a rear loading cargo carrying body with an internal space approximately 14' x 10' x 6'; this was not part of the design for the full size aircraft. With construction under way, another modification was made (but not disclosed to R.L.M.). This consisted of removing the nose of the cargo body, replacing the nose wheel by wheels on either side of the body and putting a large venturi tube with a 2m x 2.7m throat inside to form a flying wind tunnel. They expected to get about 500 mph airspeed in the throat combined with low turbulence – this they proposed to check by the sphere drag method. Later they hoped to be able to test models of their aircraft which could be made of wood because of the absence of dust in the airstream.
Construction was proceeding at Gottingen and was 50% complete at the cessation of hostilities. The steel tube framework for the venturi center section was finished.
Estimated Weight and Performance Figures
Max. all up weight as a wind tunnel 9,000 kg
Max. all up weight as a cargo carrier
Without takeoff assistance 15,000 kg
With rocket assisted takeoff 20,000 kg
At 23,000 kg the sea level rate of climb at full power would be zero.
At 9,000 kg rate of climb at 180 kph was expected to be 6.5 – 7 m/sec.
Estimated trimmed CLmax's were
No Flaps 1.4
With Flaps 1.6
CL for Takeoff 1.1
Aerodynamic Design
The design of the wing and controls was similar to that of the Horten IV. Washout was large, 7°, to give trim without elevator deflection at cruising CL. Elevons were the three stage type with 35% Frise nose on the outer flap, and 22% on the middle and inner flaps. Compensating geared tabs which could also be used a longitudinal trimmers were fitted to the inner flaps. Maximum control deflections were a follows:
(Note: All figures in degrees)
.. ------- PORT ------- --------- STARBOARD ------
CASE OUTER CENTER INNER INNER CENTER OUTER
Stick fwd. central 5 12 15 15 12 5
Stick back central -10 -18 -10 or -15 -10 or -15 -18 -10
Stick central to port -30 -15 -8 12 10 5
Stick central to stbd. 5 10 +12 -8 -15 -30
Trailing edge split flaps with a constant chord of 80 cm were to be fitted between the engines.
Drag rudders were of the H VII "trafficator" type with vent hole balance plus spring centering. Projection was about 1 meter.
Wing sections are shown in Fig. 18. Root thickness is about 16%, with the usual reflexed center-line, graded to an 8% symmetrical tip section.
Structure
Wing structure was in seven parts; a welded steel center section with pilot and co-pilots seat and three outer wooden wing panels per side. The wooden structure was of single spar D-tube form with subsidiary trailing edge ribs.
At the factory in Gottingen the center section was found in a semi-complete state, D-noses for the inboard wing panels were finished and spars and ply noses for the outer panels were under construction. Much of the work on components such as engine bearers, petrol systems, undercarriage etc., had been completed and the six engines were in crates at the works, with one spare. Unfortunately all drawings had been taken and many of them seem to have been buried by Horten employees near Kilenburg, in the Russian sector.
Undercarriage
The fixed main wheels were arranged in tandem pairs on either side of the fuselage and took 85% of the static weight of the aircraft. The castering nose wheel was retractable on the cargo version and had to be mounted on a stalky strut because of the high wing layout. Static ground incidence was 2.5°.
________________________________________



Here are a bunch of Horten images, most of them of the Ho IX but some others too.

Cheers, Neilster

 

[Neilster]

Here's part 2

3.11 Horten IX
General
The H IX was a single seat fighter bomber of 16 m span with twin jet engines, being a further development of the H V and H VII designs. Fig. 19 is a general arrangement drawing made from a wooden model found at Gottingen, where the first two of the type were built.
Four aircraft of the H IX type were started, designated V.1 to V.4. V.1 was the prototype, designed as a single seater with twin B.M.W. 003 jets, which were not ready when the airframe was finished. It was accordingly completed as a glider (Fig. 20) (not reproducible) and extensively test flown. D.V.L. instrumented it for special directional damping tests to determine its suitability as a gun platform. V.2 was completed (also at Gottingen) with two Juno 004 units and did 2-hours flying before crashing during a single engine landing. The pilot (Ziller) apparently landed short after misjudging his approach. V.3 was being built by Gotha at Friedrichsrodal as a prototype of the series production version. V.4 did not get beyond the project stage but was to be a two-seater night fighter with an extended nose to house the extra man (Fig. 19) (missing).
In shape, the H IX was a pure wing with increased chord at the center to give sufficient thickness to house the pilot and the jet units, which were placed close together on either side.
Aerodynamic Design
The H IX started as a private venture and the Hortens were very anxious to avoid failure so they avoided aerodynamic experiments wherever possible. A lower sweepback was used than on the H V and H VII and laminar flow wing sections were avoided as a potential source of trouble. Wing section at the junction with the center sections was 14% thick with maximum thickness at 30% and 1.8% zero Cmo camber line. At the centerline thickness was increased locally to 16% to house the crew. The tip section was symmetrical and 8% thick. Horten also believed that since the compressibility cosine correction to drag was based on the sweepback of the maximum thickness line, the ordinary section would show little disadvantage.
Wing twist was fixed by consideration of the critical Mach number of the underside of the tip section at top speed. This gave a maximum washout of 1.8°. Having fixed this, the CG was located to give trim at CL = 0.3 with elevons neutral. In deciding twist for high speed aircraft, CD values were considered in relation to local CL at operational top speed and altitude (10 km in the case of the H IX). Twist was arranged to give minimum overall drag consistent with trim requirements. The wing planform was designed to give a stall commencing at 0.3 to 0.4 of the semi-span.
Structure
Wing structure comprised a main spar and one auxiliary spar or wooden construction with ply covering. The center section was built up from welded steel tube. Wing tips were all metal. The undercarriage was completely retractable and of tricycle type the front wheel folding backwards and the main wheels inwards. The nose wheel was castering and centered with a roller cam. When resting on the ground, wing incidence was 7° and the nose wheel took about 40% of the total weight.
Engine Installation
The jet engines were installed at -2° to the root chord and exhausted on the upper surface of the wing at 70% back from the nose (Fig. 22a 22b). To protect the wings the surface was covered with metal plates aft of the jet pipe and cold air bled from the lower surface of the wing by a forward facing duct and introduced between the jet and the wing surface. The installation angle was such that in high speed flight the jest were parallel to the direction of flight.
Control System
Lateral and longitudinal control was by single stage elevon control flap with 25% Frise nose and compensating geared tap balance. (This system was also used on the H VII, see para. 4.6.) The pilots control column was fitted with a variable hinge point gadget, and by shifting the whole stick up about 2" the mechanical advantage could be doubled on the elevons for high-speed flight.
Directional control was by drag rudders. These were in two sections, slight movements of the rudder bar opening the small (outboard) section and giving sufficient control for high speed. At low speeds when courser control was necessary the large movement also opened the second spoiler, which started moving when the small one was fully open. By pressing both feet at once, both sets of spoilers could be operated simultaneously; this was stated to be a good method of steadying the aircraft on a target when aiming guns. The Hortens stated that the spoilers caused no buffeting and claimed an operating force of 1 kg for full rudder, with very little variation in speed. The operating mechanism is illustrated in Fig. 28. A change was made from the original H VII parallel link system to improve the control force characteristics. With the new system, aerodynamic forces could be closely balanced by correct venting of the spoiler web, leading the main control load to be supplied by a spring. The cover plate of the spoilers was spring loaded (Fig. 27) to form an effective seal with the rudders closed; this device was used on most Horten spoiler and dive brake designs.
On further models of the H IX it was proposed to fit the "trafficator" type rudder tried experimentally on the H VII.
Landing flaps consisted of plain trailing edge flaps (in four sections) on the wings, with a 3% chord lower surface spoiler running right across the center section, which functioned as a glide path control. The outer pair of plain flaps lowered 27° and the inner pair 30° – 35° on the glider version V.1. On V.2 mechanical trouble prevented the inner pair operating and all flying was done with the outer pair only. The center section spoiler could be used as a high speed brake and gave 1/3 g at 950 kph. No dive recovery flap was considered necessary.
Performance
Proper performance tests were not done on V.2 before its crash and top speed figures were calculated values, checked by Messerschmitts. The following figures were remembered by Reimar Horten:
Dimensions
All Up Weight, Including Ammunition and Armor 8,500 kg (18,700 lbs.)
All Up Weight, Excluding Ammunition and Armor 7,500 kg
Wing Area 52 sq.m (566 sq.ft.)
Wing Loading 33 lb./sq.ft.
Fuel (I2 Crude Oil) 2,000 kg (4,400 lbs.)
Performance at 7,500 kg (16,500 lbs.)
Takeoff Run 500 m
Takeoff Speed (10° Flap) 150 kph (95 mph)
(Note: This corresponds to a CL of 1.30 which is the stated stalling CL of the aircraft.)
Top Speed (at Sea Level) 950 kph (590 mph)
(CDo estimated to be 0.011)
Calculated ceiling was 16 km (52,000'). Engines would not work above 12 km as the burners went out.
Rate of Climb at Sea Level 22 m/sec (4,300 ft/min)
(Note: This has been checked roughly by observation.)
In tests against the Me 262 speeds of 650-700 kph (400-430 mph) were obtained on about 2/3 throttle opening. This appears to be the only flight test figure available.
Messerschmitt sent performance calculators to the Horten works to check their estimates. The method suggested by D.V.L. for getting the sweepback correction to compressibility drag was to take an area of 0.3 x the root chord squared at the center section as having no correction applied, and then apply full cosine correction over the outer wing. Sweepback angle was defined as that of the quarter chord locus. Test data was available for CDv. for zero sweepback.
The Messerschmitt method was to base sweepback on the max t/c locus and to scale Mach number by the square root cos Ø.
Stability and Control
The H IX V.1 was flown by Walter Horten, Scheidhauer and Ziller. Scheidhauer did most of the flying (30 hours) at Oranienberg, Horten and Ziller flew for about 10 hours.
D.V.L. instrumented the aircraft for drag and directional stability measurements. No drag results were obtained because of trouble with the instrument installation – apparently an incidence measuring pole was fitted which could be lowered in flight and glide path angle was obtained from the difference between attitude and incidence measurements. One day they landed without retracting the pole. Directional oscillation tests were completed successfully and an advance report was issued (10 pages of typescript) by Pinsker and Lugner fo D.V.L.

 

[Neilster]

Here's part 3 (final)

The essence of the results was that the lateral oscillation was of abnormally long period – about 8 sec. At 250 kph and damped out in about 5 cycles. At low speeds the oscillation was of "dutch roll" type but at high speed very little banking occurred. Many fierce arguments took place at D.V.L. on desirable directional stability characteristics , the Hortens naturally joining the "long period" school of thought. They claimed that the long period would enable the pilot to damp out any directional swing with rudder and keep perfectly steady for shooting. It was found that by using both drag rudders simultaneously when aiming, the aircraft could be kept very steady with high damping of any residual oscillation.
Lateral control was apparently quite good with very little adverse yaw.
Longitudinal control and stability was more like a conventional aircraft than any of the preceding Horten types and there was complete absence of the longitudinal "wiggle" usually produced by flying through gusts. Tuft tests were done to check the stall but the photographs were not good enough for much to be learned. Handling was said to be good at the stall, the aircraft sinking on an even keel. There seems to be some doubt, however, as to whether a full stall had ever taken place since full tests with varying CG and yaw had not been done. Although the stick was pulled hard back, the CG may have been too far forward to give a genuine stall.
Directional stability was said by Scheidhauer to be very good, as good as a normal aircraft. He did not discuss this statement in detail as he was obviously very hazy about what he meant by good stability and could give very little precise information about the type and period of the motion compared with normal aircraft.
Scheidhauer had flown the Me 163 as a glider and was obviously very impressed with it; he was confident enough to do rolls and loops on his first flight. We asked him how the H IX V.1 compared with the 163; he was reluctant to give an answer and said the two were not comparable because of the difference in size. He finally admitted that he preferred the 163 which was more maneuverable, and a delight to fly (he called it "spielzeug").
The H IX V.2 with jet engines was flown only by Ziller and completed about 2 hours flying before its crash. This occurred after an engine failure – the pilot undershot, tried to stretch the glide and stalled. One wing must have dropped, for the aircraft went in sideways and Ziller was killed. Before the crash a demonstration had been given against an Me 262; Horten said the H IX proved faster and more maneuverable, with a steeper and faster climb.
In spite of the crash, Horten thought the single engine performance satisfactory and said the close spacing of the jets made single engined flying relatively simple.

 

[Neilster]

Flying Wing Fighter "Horten IX"
by Doctor Reimar Horten
(as translated by: Fernando Walter Siarez, Buenos Aires, Argentina)
(The original article was titled "Ala volante Caza 'Horten IX' ", by Dr. Reimar Horten, published by Revista Nacional de Aeronautica, (today: Aeroespacio, Revista Nacional Aeronautica y Espacial) " May 1950, number 5, pages 19-20; Buenos Aires, Argentina. We thank them for allowing the translation and publication here for all to share. The article is being provided in both English and Spanish.)


The performances and qualities a modern fighter must have are very varied. In peacetime, the fighter development is always oriented towards its maximum speed, despite that there are many performances and qualities that determine its value during combat missions.
If the fighter is 100 Kilometers/hour [about 60-mph -Trans] faster than the bomber plane, it can overtake this latter and absolute speed is a secondary subject. During combat between fighters, higher speed is an advantage, as is higher climb rate and higher ceiling. Turning radius or time for a complete turn, are other performances that are not less important, to mention some of them.
To avoid combat, maximum speed is the only decisive one, but this is not the mission of a fighter. To intercept and achieve air supremacy, it is advantageous the higher starting position. If surprise factor fails, combat transforms into a "turning" combat. To be able to fly with small diameter turns, low wing loading is needed, from which a big wing results, what is advantageous for the practical ceiling. With this wing, take off and landing speeds, mainly the latter, are kept in an easy to dominate envelope and the amount of fuel carried aboard -that in jet aircraft can never be sufficiently large- allows satisfactory range values. The big wing does not decrease largely the maximum speed in jet fighters, because that is influenced only by aerodynamic design. This phenomenon comes from the fact that at such velocities, sonic speed is frequently achieved, so getting big additional drags. So, for example, the swept wing provides a mean to delay this drag increase, to much higher speeds.
Other factors of equal importance as speed, ceiling and turning radius also determine the combat value of a fighter. To describe them all will take us too far and is out of the scope of this article. I want only to remark the visibility of the aircraft. In the past, the detector was human eye, later it was the grounded radio that provided guidance until the airplane met the enemy. Today the pilot has the assurance of recognizing, even at night, an airplane flying many kilometers far, by means of the radar. In the past, planes were covered with camouflage paintings, and with the advent of radar, the already considered antique wood constructions, turned into something modern again. As reflection of electric waves on metallic surfaces is good, such is the image on the radar screen; on the contrary, on wood surfaces, that reflection is little, these resulting barely visible on the radar.
A fighter must use the surprise factor, especially at night; to do that, the plane must be built in wood, not only for the above mentioned circumstance, but also because the wood surface resistance to impacts is not necessary inferior to that of metallic surfaces, as was shown by tests. Also, those resistances are regarded of secondary importance, because with modern big gage guns, an impact means practically a total loss.
As far as landing speed is concerned, I want to say some words, because very often it is given a secondary importance: personally, I consider it very important because "cold losses" depend on it. Any loss is a victory for enemy. So, landing speed has great importance, besides the fact that it determines service possibilities in bad weather and at night. On the other hand, a pilot that has just ended a combat cannot be asked for high skill performances, needed with high landing speeds. Another point deserving mention, is that practice demonstrated that during a war, type specialization cannot be kept: the fighter drops bombs, takes part in ground combats, makes night interception and reconnaissance flights. Technology would like to solve a specific problem; anyway, it has to design the fighter as a multi-role aircraft and accept many compromises in such a way, that it must be able to carry bombs, or supplementary droppable tanks when it flies in a defensive mission; it must also be able to launch rockets, or be provided with an automatic movie camera, etc.
Guided by these thoughts, I built in 1943 the Horten IX model, from which two prototypes were built in the own firm, passing in 1944 to series construction under the license Gotha-Waggon Gotha. It is a flying wing of 16 meters span, equipped with two Junkers 004 turbine engines, built in three parts, the central wing section and two exterior parts. The central part that bears the load is 3.2 meters [10.5 ft -Trans] long and is built in steel tubing; in it the landing gear, turbines, weapons and pilot seat are fixed.
The turbines are inside the wing and receive air from the leading edge, without deflections. The cabin is put in the vertex of the sweep angle, between both motors, and is equipped with ejector seat, so as to allow the pilot to descend in parachute, without risk, at high flying speeds; besides the necessary armor, it has radio and identification instruments. Four MK 103 cannons, 30 mm gage, of 900 m/s of initial speed that produce a noticeable effect on the target and a ballistic corresponding to flight speeds. It has a hanging device for two bombs of 1000 Kilograms each, or for two droppable supplementary tanks, also of 1000 kilograms each. Its range is of 4000 Kilometers with 2400 kilograms of fuel in the wing, but it could be extended considering the very improved fuel consumption of today.
The landing gear, with nose wheel, had been designed for the aggravated conditions of night flying and was retractable to the wing center section. In spite of the low landing speed, of 140 kilometers per hour [87 mph -Trans], a detachable drag parachute had been installed, which allowed very short landing runs. In the center section also is installed a aerodynamic brake that permits a rapid adjust of the own speed to the enemy's own one, and that can be also used for landing. The cover shells are wood "monocoque" parts, easy to dismount for maintenance of the engines [and of ] the weapons. The second model was a two place one for night flights and training. The outer wing parts, completely built in wood, are of single spar construction. The leading edge is built in shaped wood, this is, milled wood, mixed with adhesive and then pressed to the definitive shape. By means of this construction method, a high quality product of any shape and size, can be made. The spar that transmits the forces from the wing fitting to the "monocoque", houses in its interior the command push rods. All wing space must be filled with fuel, using very simple rubber bags, attached to the monocoque. The rudders, mounted as brakes at the wing tips, produce a safe effect at any speed, and -by means of some manipulations- can also serve as elevators, so as to assure, even in supersonic flight (it can happen in a down pitch) total dominion of the plane.
After five years have passed since the last construction in Germany, I can demonstrate that the Horten IX has not been surpassed by more recent constructions. Speed records are, today as yesterday, over 960 Kilometers an hour [596 mph -Trans], its maximum speed, but the general design combination has not been excelled. The fact is that the construction principles should have been guided only by the physical phenomena arising from experiments with other built airplanes, without copying them. The contrast to this is the conventionally built airplane, resulting from the average of several ones, to be built

 

[Neilster]

In 1943 the all-wing Horten 229 promised spectacular performance and the Luftwaffe (German Air Force) chief, Hermann Göring, allocated half-a-million Reich Marks to the brothers Reimar and Walter Horten to build and fly several prototypes. Numerous technical problems beset this unique design and the only powered example crashed after several test flights but the airplane remains one of the most unusual combat aircraft tested during World War II. (Note to the reader: Horten used roman numerals to identify his designs and he followed the German aircraft industry practice of using 'Versuch,' literally test or experiment, numbers to describe pre-production prototypes built to test and develop a new design into a production airplane. The Horten IX design became the Horten Ho 229 aircraft program after Göring granted the project official status in 1943 and the technical office of the Reichsluftfahrtministerium assigned to it the design number 229. This is also the nomenclature used in official German documents).
The idea for the Horten IX grew first in the mind of Walter Horten when he was serving in the Luftwaffe as a fighter pilot engaged in combat in 1940 during the Battle of Britain. Horten was the technical officer for Jadgeschwader (fighter squadron) 26 stationed in France. The nature of the battle and the tactics employed by the Germans spotlighted the design deficiencies of the Messerschmitt Bf 109, Germany 's most advanced fighter airplane at that time. The Luftwaffe pilots had to fly across the English Channel or the North Sea to fulfill their missions – escorting German bombers and attacking British fighters – and Horten watched his unit lose many men over hostile territory at the very limit of the airplane's combat radius. Often after just a few minutes flying in combat, the Germans frequently had to turn back to their bases or run out of fuel and this lack of endurance severely limited their effectiveness. The Messerschmitt was also vulnerable because it had just a single engine. One bullet could puncture almost any part of the cooling system and when this happened, the engine could continue to function for only a few minutes before it overheated and seized up. Walter Horten came to believe that t he Luftwaffe needed a new fighter designed with performance superior to the Spitfire, Britain's most advanced fighter. The new airplane required sufficient range to fly to England, loiter for a useful length of time and engage in combat, and then return safely to occupied Europe. He understood that only a twin-engine aircraft could give pilots a reasonable chance of returning with substantial battle damage or even the loss of one engine.

 

[Neilster]

Since 1933, and interrupted only by military service, Walter and Reimar had experimented with all-wing aircraft. With Walter's help, Reimar had used his skills as a mathematician and designer to overcome many of the limitations of this exotic configuration. Walter believed that Reimar could design an all-wing fighter with significantly better combat performance than the Spitfire. The new fighter needed a powerful, robust propulsion system to give the airplane great speed but also one that could absorb damage and continue to function. The Nazis had begun developing rocket, pulse-jet, and jet turbine configurations by 1940 and Walter's role as squadron technical officer gave him access to information about these advanced programs. He soon concluded that if his brother could design a fighter propelled by two small and powerful engines and unencumbered by a fuselage or tail, very high performance was possible.
At the end of 1940, Walter shared his thoughts on the all-wing fighter with Reimar who fully agreed with his brother's assessment and immediately set to work on the new fighter. Fiercely independent and lacking the proper intellectual credentials, Reimar worked at some distance from the mainstream German aeronautical community. At the start of his career, he was denied access to wind tunnels due to the cost but also because of his young age and lack of education, so he tested his ideas using models and piloted aircraft. By the time the war began, Reimar actually preferred to develop his ideas by building and testing full-size aircraft. The brothers had already successfully flown more than 20 aircraft by 1941 but the new jet wing would be heavier and faster than any previous Horten design. To minimize the risk of experimenting with such an advanced aircraft, Reimar built and tested several interim designs, each one moderately faster, heavier, or more advanced in some significant way than the one before it.
Reimar built the Horten V b and V c to evaluate the all-wing layout when powered by twin engines driving pusher propellers. He began in 1941 to consider fitting the Dietrich-Argus pulse jet motor to the Horten V but this engine had drawbacks and in the first month of 1942, Walter gave his brother dimensioned drawings and graphs that charted the performance curves of the new Junkers 004 jet turbine engine (this engine is also fitted to these NASM aircraft: Messerschmitt Me 262, Arado Ar 234, and the Heinkel He 162). Later that year, Reimar flew a new design called the Horten VII that was similar to the Horten V but larger and equipped with more powerful reciprocating engines. The Horten VI ultra-high performance sailplane also figured into the preliminary aerodynamic design of the jet flying wing after Reimar tested this aircraft with a special center section.
Walter used his personal connections with important officials to keep the idea of the jet wing alive in the early stages of its development. General Ernst Udet, Chief of Luftwaffe Procurement and Supply and head of the Technical Office "was the man who protected this idea and followed this idea" for the all-wing fighter for almost a year until Udet took his own life in November 1941. At the beginning of 1943, Walter heard Göring complain that Germany was fielding 17 different types of twin-engine military airplanes with similar, and rather mediocre, performance but parts were not interchangeable between any two designs. He decreed that henceforth he would not approve for production another new twin-engine airplane unless it could carry 1,000 kg (2,210 lb) of bombs to a 'penetration depth' of 1,000 km (620 miles, penetration depth defined as 1/3 the range ) at a speed of 1,000 km/h (620 mph). Asked to comment, Reimar announced that only a warplane equipped with jet engines had a chance to meet those requirements.

 

[Neilster]

In August Reimar submitted a short summary of an all-wing design that came close to achieving Göring's specifications. He issued the brothers a contract, and then demanded the new aircraft fly in 3 months! Reimar responded that the first Horten IX prototype could fly in six months and Göring accepted this schedule after revealing his desperation to get the new fighter in the air with all possible speed. Reimar believed that he had boosted the Reichsmarschall's confidence in his work after he told him that his all-wing jet bomber was based on data obtained from bona fide flight tests with piloted aircraft.
Official support had now been granted to the first all-wing Horten airplane designed specifically for military applications but the jet bomber that the Horten brothers began to design was much different from the all-wing pure fighter that Walter had envisioned nearly four years earlier as the answer to the Luftwaffe's needs for a long-range interceptor. Hencefourth, the official designation for airplanes based on the Horten IX design changed to Horten Ho 229 suffixed with 'Versuch' numbers to designate the various prototypes.
All versions of the Ho 229 resembled each other in overall layout. Reimar swept each half of the wing 32 degrees in an unbroken line from the nose to the start of each wingtip where he turned the leading edge to meet the wing trailing edge in a graceful and gradually tightening curve. There was no fuselage, no vertical or horizontal tail, and with landing gear stowed (the main landing gear was fixed but the nose wheel retracted on the first prototype Ho 229 V1), the upper and lower surface of the wing stretched smooth from wingtip to wingtip, unbroken by any control surface or other protuberance. Horten mounted elevons (control surfaces that combined the actions of elevators and ailerons ) to the trailing edge and spoilers at the wingtips for controlling pitch and roll, and he installed drag rudders next to the spoilers to help control the wing about the yaw axis. He also mounted flaps and a speed brake to help slow the wing and control its rate and angle of descent. When not in use, all control surfaces either lay concealed inside the wing or trailed from its aft edge. Parasite or form drag was virtually nonexistent. The only drag this aircraft produced was the inevitable by-product of the wing's lift. Few aircraft before the Horten 229 or after it have matched the purity and simplicity of its aerodynamic form but whether this achievement would have led to a successful and practical combat aircraft remains an open question.
Building on knowledge gained by flying the Horten V and 'VII, Reimar designed and built a manned glider called the Horten 229 V1 which test pilot Heinz Schiedhauer first flew 28 February 1944. This aircraft suffered several minor accidents but a number of pilots flew the wing during the following months of testing at Oranienburg and most commented favorably on its performance and handling qualities. Reimar used the experience gained with this glider to design and build the jet-propelled Ho 229 V2.
Wood is an unorthodox material from which to construct a jet aircraft and the Horten brothers preferred aluminum but in addition to the lack of metalworking skills among their team of craftspersons, several factors worked against using the metal to build their first jet-propelled wing. Reimar's calculations showed that he would need to convert much of the wing's interior volume into space for fuel if he hoped to come close to meeting Göring's requirement for a penetration depth of 1,000 km. Reimar must have lacked either the expertise or the special sealants to manufacture such a 'wet' wing from metal – whatever the reason, he believed that an aluminum wing was unsuitable for this task. Another factor in Reimar's choice of wood is rather startling: he believed that he needed to keep the wing's radar cross-section as low as possible. "We wished," he said many years later, "to have the [Ho 229] plane … that would not reflect [radar signals]" and Horten believed he could meet this requirement more easily with wood than metal. Many questions about this aspect of the Ho 229 design remain unanswered and no test data is available to document Horten's work in this area. The fragmentary information that is currently available comes entirely from anecdotal accounts that have surfaced well after World War II ended.

 

[Neilster]

As they developed the '229, the Horten brothers measured the wing's performance against the Messerschmitt Me 262 jet fighter. According to Reimar and Walter, the Me 262 had a much higher wing loading than the Ho 229 and the Messerschmitt required such a long runway for take off that only a few airfields in Germany could accommodate it. The Ho 229 wing loading was considerably lower and this would have allowed it to operate from airfields with shorter runways. Reimar also believed, perhaps naively, that his wing could take off and land from a runway surfaced with grass but the Me 262 could not. If these had been true, a Ho 229 pilot would have had many more airfields from which to fly than his counterpart in the Messerschmitt jet.
Successful test flights in the Ho 229 V1 led to construction of the first powered wing, the Ho 229 V2, but poor communication with the engine manufacturers caused lengthy delays in finishing this aircraft. Horten first selected the 003 jet engine manufactured by BMW but then switched to the Junkers 004 power plants. Reimar built much of the wing center section based on the engine specifications sent by Junkers but when two motors finally arrived and Reimar's team tried to install them, they found the power plants were too large in diameter to fit the space built for them. Months passed while Horten redesigned the wing and the jet finally flew in mid-December 1944.
Full of fuel and ready to fly, the Horten Ho 229 V2 weighed about nine tons and thus it resembled a medium-sized, multi-engine bomber such as the Heinkel He 111. The Horten brothers believed that a military pilot with experience flying heavy multi-engine aircraft was required to safely fly the jet wing and Scheidhauer lacked these skills so Walter brought in veteran Luftwaffe pilot Lt. Erwin Ziller. Sources differ between two and four on the number of flights that Ziller logged but during his final test flight an engine failed and the jet wing crashed, killing Ziller.
According to an eyewitness, Ziller made three passes at an altitude of about 2,000 m (6,560 ft) so that a team from the Rechlin test center could measure his speed using a theodolite measuring instrument. Ziller then approached the airfield to land, lowered his landing grear at about 1,500 m (4,920 ft), and began to fly a wide descending spiral before crashing just beyond the airfield boundary. It was clear to those who examined the wreckage that one engine had failed but the eyewitness saw no control movements or attempt to line up with the runway and he suspected that something had incapacitated Ziller, perhaps fumes from the operating engine. Walter was convinced that the engine failure did not result in uncontrollable yaw and argued that Ziller could have shut down the functioning engine and glided to a survivable crash landing, perhaps even reached the runway and landed without damage. Walter also believed that someone might have sabotaged the airplane but whatever the cause, he remembered "it was an awful event. All our work was over at this moment." The crash must have disappointed Reimar as well. Ziller's test flights seemed to indicate the potential for great speed, perhaps a maximum of 977 km/h (606 mph). Although never confirmed, such performance would have helped to answer the Luftwaffe technical experts who criticized the all-wing configuration.
At the time of Ziller's crash, the Reich Air Ministry had scheduled series production of 15-20 machines at the firm Gotha Waggonfabrik Flugzeugbau and the Klemm company had begun preparing to manufacture wing ribs and other parts when the war ended.

 

[Neilster]

Horten had planned to arm the third prototype with cannons but the war ended before this airplane was finished. Unbeknownst to the Horten brothers, Gotha designers substantially altered Horten's original design when they built the V3 airframe. For example, they used a much larger nose wheel compared to the unit fitted to the V2 and Reimar speculated that the planned 1,000 kg (2,200 lb) bomb load may have influenced them but he believed that all of the alterations that they made were unnecessary.
The U.S. VIII Corps of General Patton's Third Army found the Horten 229 prototypes V3 through V6 at Friedrichsroda in April 1945. Horten had designed airframes V4 and V5 as single-seat night fighters and V6 would have become a two-seat night fighter trainer. V3 was 75 percent finished and nearest to completion of the four airframes. Army personnel removed it later and shipped it to the U.S., via the Royal Aircraft Establishment at Farnborough, England. Reports indicate the British displayed the jet during fall 1945 and eventually the incomplete center section arrived at Silver Hill (now the Paul E. Garber Facility in Suitland, Maryland ) about 1950. There is no evidence that the outer wing sections were recovered at Friedrichsroda but members of the 9th Air Force Air Disarmament Division found a pair of wings 121 km (75 miles) from this village and these might be the same pair now included with the Ho 229 V3.
Reimar and Walter Horten demonstrated that a fighter-class all-wing aircraft could successfully fly propelled by jet turbine engines but Ziller's crash and the end of the war prevented them from demonstrating the full potential of the configuration. The wing was clearly a bold and unusual design of considerable merit, particularly if Reimar actually aimed to design a stealthy bomber but as a tailless fighter-bomber armed with massive 30mm cannon placed wide apart in the center section, the wing would probably have been a poor gun platform and found little favor among fighter pilots. Walter argued rather strenuously with his brother to place a vertical stabilizer on this airplane. Like most of the so-called 'Nazi wonder weapons,' the Horten IX was an interesting concept that was poorly executed.
Although the Garber Facility was closed to public tours in 2003, requests to view the extraordinary Horten Ho 229 V3 have continued to pour in to the Museum staff. Curators and restoration specialists hope to begin working on this artifact when the restoration shop complex is finished at the Steven F. Udvar-Hazy Center during the next several years.

Cheers, Neilster